1. Field of the Invention
The present invention relates to a medical device guiding system having a position detecting function of detecting a position of a medical device, which is guided to move in a body cavity, a medical device guiding method, and a method for creating a look-up table to be used in the medical device guiding system.
2. Description of the Related Art
Conventionally, as one of medical devices that observe inside a subject, a capsule medical device such as a capsule endoscope has been put to practical use. The capsule endoscope is introduced into a body cavity, and captures images of a desired target region by an image pick-up device incorporated therein at the time of passing through the body cavity. In this case, because an imaging range (angle of view) of the image pick-up device is fixed, a position or direction of the capsule endoscope needs to be guide-controlled so that a desired region to be observed comes within an imaging area. Therefore, as a guiding system therefor, for example, there is a system disclosed in International Publication No. WO05/112733. According to International Publication No. WO05/112733, the position and direction of a capsule endoscope are controlled by causing a guiding magnetic field, by a guiding coil arranged to surround six faces around the capsule endoscope having a built-in magnet, to act on the magnet.
To perform such guiding control as desired, it is essential provide a position detecting device that accurately detects a current position of the capsule endoscope. Therefore, in International Publication No. WO05/112733, an LC resonance circuit including a coil and a capacitor is provided inside the capsule endoscope, the LC resonance circuit is resonated by a magnetic field emitted toward a position detection area of the capsule endoscope, to detect the magnetic field of a specific frequency newly generated due to resonance by a plurality of magnetic field sensors arranged around the position detection area, and the position of the capsule endoscope is acquired from field strength detected by each magnetic field sensor.
Furthermore, as described in U.S. Pat. No. 6,493,573 and Japanese Laid-open Patent Publication No. 2006-75533, the position of the capsule endoscope can be detected also by detecting a magnetic field emitted from outside toward the position detection area of the capsule endoscope by a magnetic field sensor incorporated in the capsule endoscope.
The position detection methods described in International Publication No. WO05/112733, U.S. Pat. No. 6,493,573, and Japanese Laid-open Patent Publication No. 2006-75533 mentioned above use a fact that magnetic field distribution created in space by a coil can be calculated in theory. Therefore, it is not desirable that a conductor or a magnetic body that will possibly disturb the magnetic field distribution exists in the position detection area.
Therefore, U.S. Pat. No. 6,493,573 discloses a method for correcting data by acquiring a time constant of an eddy current by a magnetic field of a different frequency, because position detection accuracy decreases if the eddy current flows into an interfering body existent in a position detection area. Furthermore, there is also disclosed a method in which magnetic field distribution generated by calculating and taking into consideration an effect by an interfering body (a shield member) is held in a look-up table (LUT) and read.